The nacelle of a wind turbine is a confined area which comprises several heavy wind turbine components, such as gears, shafts, generators, etc., which from time to time need maintenance, repair, or even replacement, wherefore internal lifting equipments are arranged in connection with the nacelle for supporting said handling.
For instance an internal travelling crane is known in the prior art. The crane consists of two suspension rails, which are connected to the nacelle. In relation to the rails, a movable cross beam is arranged, and a hoisting device is arranged movably on the cross beam. The two suspension rails are arranged at each end of the nacelle so that they are parallel in relation to each other. Accordingly, the cross beam extends between and is movably coupled to the two suspension rails so that the cross beam can be moved along a longitudinal extension of the suspension rails.
Often the nacelle is not completely rectangular in shape, whereby some of the area below the crane is not covered by the crane, and thereby the handling of the equipment in these areas is difficult. In the prior art, this is partly solved by the cross beam being rotatable about a vertical axis of the movable couplings to the suspension rails so that the cross beam can extend between the suspension rails in an angle different from 90 degrees. However, since the necessary length of the cross beam may vary according to the extension angle, the cross beam is arranged displaceable in one of the movable couplings. This has the consequence that space has to be arranged on the opposite side of one of the suspension rails so that the cross beam can extend beyond the suspension rail when the cross beam is placed in the shortest distance between the two suspension rails, whereby some of the areas in the nacelle are not covered by the crane.
Also, since the above-mentioned cross beam is displaceable and is rotatable about vertical axis of the movable couplings to the suspension rails, it has been observed that during use of the crane and especially in circumstances wherein the cross beam extends with an angle different from 90 degrees as well as being exerted for load, the cross beam may have a tendency for tilting whereby the movable couplings also may be exerted with unintended forces which may have the disadvantages that the movable couplings cannot move along the suspension rails as intended. This reduces the reliability of the crane.
It is furthermore known to have a crane structure wherein one suspension beam is curved and the other suspension is a linear beam. The cross beam is in this known crane structure movably connected to the curved suspension beam and is stationary, hingedly connected to the linear beam and is adapted to rotate about said hinge. Since the cross beam is stationary, hingedly connected to the linear beam, the crane structure has the disadvantage that it does not cover the entire area of the nacelle.